Analysis of a magnetic injection valve, including oscillograms of current and voltage.
| Identifier | ExFiles\Box 158\5\ scan0037 | |
| Date | 22th April 1939 | |
| MAGNETIC INJECTION VALVE 533 Fig. 6. Oscillograms of the current through the nozzle A. {Mr Adams} (Left) 1300 mf condenser charge. B. (Right) 1300 mf condenser with charge throttled to 600 mf by means of a variable resistance in the circuit. latory circuit indicates that the period tₒ the valve is open is smaller, and hence the fuel delivered at constant pressure is less, than for the case of the critically damped circuit tₐ. In the oscillatory circuit the delay in nozzle opening is slightly less than for the critically damped circuit. Fig. 5 indicates that the operating characteristics of the valve may be varied over quite a range by slight changes in the constants of the discharge circuit. For example, by increasing the voltage, decreasing the value of the rated condenser capacity, and changing the circuit resistance, the valve could be made to open twice or three times per cycle. This manner of operation would make the successive injections of the cycle decrease. Since this type of injection may not be desirable, the analysis might be considered as giving the limiting values of the constants of the circuit. On the other hand, it is often considered desirable to inject a very small charge of fuel into the cylinder before the main charge enters, thus initiating the combustion cycle. This characteristic may be obtained with the magnetically actuated valve by introducing a coupling inductance and a second tuned circuit. Throttling, or the control of the quantity of fuel injected per cycle, is easily obtained by means of the resistance in the charging circuit. The circuit acts in an identical manner for each cycle, and since the oil pressure is maintained constant to the valve, the amount of fuel discharged and the form of the spray is very consistent for successive cycles. A series of oscillograms taken of the current through the valve, the voltage across the valve, and the voltage across the condenser, are shown in Figs. 6, 7, and 8. The current curves show the very short de-lay in opening, as indicated by the nearly vertical rise of current from zero to the break in the curve. The break is due to the counter voltage generated by the change in inductance resulting from the motion of the valve plunger. The point at which the needle seats is indicated by the flat part of the curve on the decreasing side of the peak. Fig. 7. Oscillogram of voltage across the valve The curve of voltage across the valve is nearly identical in form to the time rate of change of the current curve. This indicates that the resistance of the valve circuit is quite low, as compared with its inductance. The points at which the needle lifted and seated were quite distinct on the screen of the cathode ray oscillograph, but since the motion of the spot on the screen was so rapid, the resulting break is barely visible on the photographic record. The effect of changing the throttling resistance is shown in the oscillogram of the voltage across the condenser Fig. 8. Without the throttling resistance in the circuit, the condenser charges to full voltage very rapidly and remains at constant voltage to the point of discharge. Increasing the throttling resistance requires a longer time for the condenser to reach full charge. The voltage build-up with increased resistance is shown in Fig. 8B, which also shows the small switching time from charge to discharge, as indicated by the flat portion at the top of the curve. Spray Development The investigation of the electrical characteristics of the magnetically actuated spray valve indicates that successive operating cycles are identical. It is desirable for smooth-engine operation that the spray be also reproducible. Therefore, knowing that the pressure at the valve is constant, it is reasonable to assume that successive sprays will be nearly identical in all respects. In order to investigate the development of the spray, photographs were taken at intervals of one degree cam angle. This means that a complete picture of spray development represents several hundred injections, since approximately one hundred injections occurred between successive photographs. If successive Fig. 8. Oscillograms of voltage across the condenser A. {Mr Adams} (Left) Voltage across condenser without throttling resistance in the circuit. B. (Right) Voltage across the condenser with throttling resistance in the circuit. Automotive Industries April 22, 1939 | ||
From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).